North Cascades Geology

Minerals And Rocks

Quartz crystals (silicon dioxide).

Fundamental to understanding mountain geology is the nature of minerals and rocks, for the mountains are made out of rocks, and the rocks are made out of minerals. The simplest, most widely known and distributed mineral is quartz (silicon dioxide), which is made up of the elements silicon and oxygen. Most of the rocks in the North Cascades, and elsewhere for that matter, are made up of about seven types of silicate minerals, all of which which contain a double dose of quartz (as silicon tetroxide), combined with various elements. (See Common Rock-Forming Minerals and Their Elements).

Rocks are classified according to the ways they
are made and the proportion of various minerals
that form them. Many rock names reflect their
composition.

Types of Rocks

All rocks belong to one of three major groups: igneous, sedimentary, or metamorphic. Many different rocks representing these three groups occur in the North Cascades.

Material in this site has been adapted from a book,
Geology of the North Cascades: A Mountain Mosaic by R. Tabor
and R. Haugerud, of the USGS, with drawings by Anne Crowder. It is published
by The Mountaineers, Seattle.